Thank you for asking this question on the Microsoft Q&A Platform.
You did a great investigation, and you are correct in your approach. Unfortunately, they are not alternative options, in your case you must:
- Install a Windows Server 2016; or
- Complete the migration of your Exchange, so you could use Cloud Sync.
Hope this helps!
Accept Answer and Upvote, if any of the above helped, this thread can help others in the community looking for remediation for similar issues.
NOTE: To answer you as quickly as possible, please mention me in your reply.